Process and system for recycling epoxy thermosetting resin

Abstract

The present invention relates to a process and system for recycling an epoxy thermosetting resin containing cleavable bonds, said process comprising dissolving the epoxy thermosetting resin using an acid solution and devolatilizing the acid solution from a thermoplastic acidic mixture to produce a thermoplastic component. Such a process enables the recovery of a recyclable thermoplastic component and optionally a recyclable reinforcing matrix component. Such a process comprises the steps of: dissolving the epoxy thermosetting resin in an acid solution under heated conditions to produce a thermoplastic mixture; optionally filtering the thermoplastic mixture to separate the reinforcing matrix component from the thermoplastic solution; and devolatilizing the thermoplastic solution to obtain a recyclable thermoplastic component.

Description

Technology Field

[0001] The present invention relates to a process and system for recycling an epoxy thermoset containing cleavable bonds by devolatizing the acid solution from a thermoplastic acidic mixture after using the acid solution, wherein the process enables the recovery and reuse of a recyclable thermoplastic component and optionally a recyclable reinforcement matrix component. Background Technology

[0002] Epoxy resins are an important class of thermosetting compounds. They are economical, possess low toxicity, and offer a unique combination of thermal, mechanical, and chemical resistance properties that cannot be achieved with other thermosetting resins. They exhibit high chemical and solvent resistance, low shrinkage rates, and excellent adhesion to various substrates. Epoxy resins are also used in the manufacture of fiber-reinforced polymer composites.

[0003] Epoxy thermosetting resins have a wide range of applications and are widely used in automobiles, aerospace and defense equipment, wind mills, structural adhesives, electronics, ceramic manufacturing, and microelectronic packaging. Extensive applications exist in civil engineering and construction, such as structural components, epoxy cement, floor coatings, metal coatings, marine coatings, paints, decorative art, and lacquer. Due to their superior performance, epoxy resins are also preferred for coating applications, such as can coatings, powder coatings, and food and packaging coatings.

[0004] However, recycling conventional epoxy resins is difficult because, after heat curing, the resin becomes infusible and insoluble in common solvents. In particular, once cured, epoxy resin does not melt under heat, making it difficult to reuse as a resin material. Consequently, the manufacture of conventional epoxy resin-cured products, as well as products to which epoxy resin-cured products are attached or applied, generates a large amount of waste. Furthermore, after the product reaches the end of its life, recovering and reusing valuable components from the polymer epoxy matrix or recycling the epoxy itself presents a challenge. Generally, all components are disposed of and lost through incineration and landfill. These disposal methods cause irreversible damage and environmental pollution.

[0005] A type of recyclable epoxy has been developed to enable the depolymerization of epoxy resins, wherein the thermosetting resin polymer has cleavable bonds. Recyclable epoxy is prepared by using a recyclable acid-unstable curing agent with a conventional epoxy or by using a recyclable epoxy resin with a conventional curing agent. The resulting epoxy thermosetting resin polymer has cleavable bonds that allow for depolymerization, thereby enabling recycling. In the case of epoxy composite materials, after depolymerization, the epoxy resin dissolves, and other materials such as metals, glass fibers, and carbon fibers can be separated, recovered, and recycled.

[0006] Prior art methods for recycling recyclable thermosetting resins and composites utilize decomposers such as acids and solvents. These prior art methods for recycling recyclable thermosetting resins employ an NaOH neutralization step in which the acid used to dissolve the thermoplastic component of the recyclable epoxy thermosetting resin is neutralized using NaOH. This step is undesirable because it generates waste, such as sodium acetate, which cannot be treated as sewage waste and instead requires specialized treatment. Furthermore, these prior art methods are batch processes that are not industrially relevant and cannot be easily scaled up. Therefore, there is a need for an industrially and commercially viable, effective, and scalable recycling process that allows for the recovery of components of epoxy thermosetting resins and their composites while reducing environmental impact.

[0007] Therefore, there remains an opportunity to develop a method for recycling epoxy polymers and composites thereof that solves one or more problems related to methods known in the art or at least provides a viable alternative to such methods.

[0008] According to one embodiment, the present invention is a process for recycling an epoxy thermosetting resin comprising at least one recyclable component, wherein

[0009] i. A step of inducing the formation of a thermoplastic mixture by dissolving an epoxy thermosetting resin in an acid solution under heated conditions of 50 to 110°C;

[0010] ii. A step of filtering the thermoplastic mixture to separate the reinforcing matrix component from the thermoplastic solution; and

[0011] iii. A process comprising the step of devolatilizing a thermoplastic solution to remove an acid solution in order to obtain a recyclable thermoplastic component.

[0012] According to another embodiment, the present invention is a system for recycling an epoxy thermosetting resin comprising at least one recyclable component, wherein

[0013] i. A dissolution subsystem configured to dissolve an epoxy thermosetting resin in an acid solution under heated conditions to form a thermoplastic mixture;

[0014] ii. A filtering subsystem configured to filter the thermoplastic mixture to separate the reinforcing matrix component from the thermoplastic solution; and

[0015] iii. A system comprising a devolatizing subsystem configured to remove an acid solution from a thermoplastic solution to obtain a recyclable thermoplastic component, and

[0016] Here, the devolatilization subsystem includes an extruder, a falling film evaporator, a distillation unit, or a combination thereof.

[0017] According to another embodiment, the present invention is a process for recycling an epoxy thermosetting resin containing a recyclable component, wherein

[0018] i. a step of dissolving an epoxy thermosetting resin in an acidic solution to induce at least partial dissolution of the epoxy thermosetting resin to form a thermoplastic mixture; and

[0019] ii. A process comprising the step of devolatilizing a thermoplastic mixture to remove an acid solution and obtaining a recyclable thermoplastic component containing a reinforcing matrix component.

[0020] According to another embodiment, the present invention is a system for recycling an epoxy thermosetting resin containing a recyclable component, wherein

[0021] i. A dissolution subsystem configured to dissolve an epoxy thermosetting resin in an acidic solution to form a thermoplastic mixture; and

[0022] ii. A system comprising a devolatilization subsystem configured to remove an acid solution from a thermoplastic mixture to obtain a recyclable thermoplastic component including a reinforcing matrix component, and

[0023] Here, the devolatilization subsystem includes an extruder, a falling film evaporator, a distillation unit, or a combination thereof. Brief explanation of the drawing

[0024] Specific embodiments of the present invention will be referenced, and such examples may be illustrated in the accompanying drawings. These drawings are for illustrative purposes only and are not intended to be limiting. Although the present invention is generally described in the context of these specific embodiments, it should be understood that the scope of the invention is not intended to be limited to these particular embodiments. FIG. 1 illustrates a specific example of the process of the present invention for recycling an epoxy thermosetting resin, in which the epoxy thermosetting resin is completely dissolved (dissolution process). FIG. 2 illustrates a specific example of the process of the present invention for recycling an epoxy thermosetting resin in which the epoxy thermosetting resin is at least partially dissolved (non-dissolving process). FIG. 3 illustrates a specific example of the system of the present invention for recycling epoxy thermosetting resin, in which the epoxy thermosetting resin is completely dissolved (dissolution process apparatus). FIG. 4 illustrates a specific example of a system of the present invention for recycling epoxy thermosetting resin, in which the epoxy thermosetting resin is at least partially dissolved (non-dissolving process apparatus). Figure 5a shows graphic data on the effect of different concentrations of acid over time on the recycling of epoxy waste at 60°C. Figure 5b shows graphic data on the effect of different concentrations of acid over time on the recycling of epoxy waste at 80°C. Figure 5c shows graphic data on the effect of different concentrations of acid over time on the recycling of epoxy waste at 100°C. Specific details for implementing the invention

[0025] In the following detailed description, embodiments are described in sufficient detail to enable a person skilled in the art to practice the invention, and it will be understood that other embodiments may be utilized and modifications may be made without departing from the scope of the invention. To avoid details that are not necessary for a person skilled in the art to practice the embodiments described herein, the description may omit specific information known to a person skilled in the art. Accordingly, the description and drawings should be considered illustrative rather than restrictive, and all such modifications are intended to be included within the scope of this teaching. The singular form should be understood to include a plurality of referents unless otherwise specified in the context. It should be emphasized that the term “comprising / comprising” as used herein is used to specify the presence of a mentioned feature, integer, step, or component, but does not exclude the presence or addition of one or more other features, integers, steps, components, or groups thereof.

[0026] The present invention, in one embodiment, is a process for recycling an epoxy thermosetting resin comprising at least one recyclable component, wherein

[0027] A step of inducing the formation of a thermoplastic mixture by dissolving an epoxy thermosetting resin in an acid solution under heated conditions of 50 to 110°C;

[0028] A step of filtering a thermoplastic mixture to separate a reinforcing matrix component from a thermoplastic solution; and

[0029] The present invention aims to solve the disadvantages of the aforementioned prior art by providing a process that includes the step of devolatilizing a thermoplastic solution to remove an acid solution in order to obtain a recyclable thermoplastic component.

[0030] The above process is an industrial melting process in which the melting of an epoxy thermosetting resin leads to the formation of a thermoplastic mixture. In a preferred embodiment, such a process is carried out at 100°C. In a preferred embodiment, the epoxy thermosetting resin is reduced in size before being dissolved in an acid solution. The melting of the thermoplastic material in the acid solution is a complete melting, and the resulting thermoplastic mixture contains undissolved components, such as a reinforcing matrix component and non-recyclable components suspended in the thermoplastic solution. Filtration removes undissolved components from the thermoplastic solution. The thermoplastic material dissolved in the acid solution is recovered after removing the acid by distillation, wipe film evaporation, and / or devolatilization of the acid solution using a devolatilization extruder. The recyclable thermoplastic components obtained using the above process can be compounded or extruded by reactive extrusion to produce various grades of usable thermoplastic materials.

[0031] In one embodiment of the process, filtration further comprises separating undissolved components by centrifugation, manual sorting, optical sorting, or a combination thereof. The undissolved components may be sorted for recovery and reuse or disposed of. The reinforcing matrix components that are separately removed and recycled are nearly as good as new materials. This allows for the recovery of nearly all or part of the value of the reinforcing material. In one embodiment of the process, the reinforcing matrix components include glass fibers, carbon fibers, aramid fibers, jute, grass, bamboo, pine, balsa, other natural fibers, and combinations thereof, and are recyclable.

[0032] In one embodiment of the dissolution process, the acid solution is acetic acid, lactic acid, propionic acid, any other aliphatic acid, any other organic acid, or a combination thereof, wherein acetic acid is present at a concentration of 5 to 70% and lactic acid is present at a concentration of 20 to 80%. According to a preferred embodiment, the acid solution is 10 to 15% acetic acid or 50% lactic acid. The recycling process is mild and preferably uses a weak acid. In one embodiment of the process, the acid solution contains a solvent selected from water, butanol, isopropanol, propanol, ethanol, methanol, benzyl alcohol, ethylene glycol, dichloromethane, tetrahydrofuran, ethyl acetate, acetone, dimethylformamide, acetonitrile, dimethyl sulfoxide, nitromethane, propylene carbonate, pentane, hexane, cyclohexane, benzene, toluene, xylene, dioxane, glyme, polyether, diethyl ether, any other nonpolar solvent, any other polar aprotic solvent, any other polar protic solvent, and combinations thereof.

[0033] All devolatilized solvents containing acid can be recycled. In one embodiment of the process, the removed acid solution, solvent, or both are recycled back into the process. In one embodiment, the process is continuous or batch-based. In a preferred embodiment, the process is continuous.

[0034] In one embodiment of the process, an epoxy thermosetting resin is prepared from a diepoxy resin and a recyclable acid-unstable curing agent, wherein the recyclable acid-unstable curing agent is an amine-based curing agent, a thiol-based curing agent, a polyamino compound, any other acid-unstable curing agent, or a combination thereof.

[0035] In one embodiment, the recyclable acid-unstable curing agent is a compound of the following formula (1):

[0036]

[0037] In the above equation, m is 2, 1, or 0; n is 2, 3, or 4; and the sum of m and n is 4;

[0038] Each R1 is independently hydrogen, alkyl, cycloalkyl, heterocyclic, heterocycloalkyl, alkenyl, cycloalkenyl, aryl, heteroaryl, alkyloxyalkyl, or alkenyl;

[0039] Each A is independently unsubstituted ethylene, propylene, isopropylene, butylene, iso-butylene, hexylene, ethylene-oxy-ethylene, ethylene-amino-ethylene, And;

[0040] Each R2 is independently -NHR3, where each R3 is independently hydrogen, alkyl, aminoalkyl, alkylaminoalkyl, cycloalkyl, heterocyclic, alkenyl, aryl, or heteroaryl; all two -OA-R2 groups can form a dioxanyl ring having four or more ring members together with the carbon atoms to which they are bonded, and one or more of the ring carbon atoms that are not the carbon atoms to which the two -OA-R2 groups are bonded are independently substituted with one or more amino groups or aminoalkyl, where each amino is independently a primary or secondary amino group.

[0041] In one embodiment, the recyclable acid-unstable curing agent is a compound of the following formula (2):

[0042]

[0043] In the above equation, q is 4, 3, 2, or 1; t is 0, 1, 2, or 3; the sum of q and t is 4;

[0044] Each case of W is independently alkylene, cycloalkylene, heterocyclylene, alkenylene, alkynylene, cycloalkenylene, arylene, or heteroarylene; each case of R5 is independently hydrogen, alkyl, cycloalkyl, heterocyclylene, alkenyl, alkynylene, cycloalkenyl, aryl, heteroaryl, aminoalkyl, aminoaryl, substituted amino group, or --OR C and, here, R C is an alkyl (e.g., methyl, ethyl), cycloalkyl, heterocyclil, alkenyl, alkynyl, cycloalkenyl, aryl (e.g., phenyl), or heteroaryl.

[0045] In one embodiment, a recyclable acid-unstable curing agent of formula (1), formula (2), or a combination thereof is used with a diepoxy resin which is a conventional diepoxy resin selected from the group comprising BPA-diglycidyl ether, BPF-diglycidyl ether, BPS-diglycidyl ether, reactive diluent, diglycidyl amine, aqueous epoxy resin, formulated epoxy resin, and combinations thereof.

[0046] In one embodiment of the process, an epoxy thermosetting resin is prepared from a recyclable epoxy resin and a curing agent, wherein the recyclable epoxy resin comprises an acid-degradable acetal, ketal, orthocarbonate, orthoester, orthosilicate, or silane linkage.

[0047] In one embodiment, the recyclable epoxy resin is a compound of the following formula (3) or formula (4):

[0048]

[0049] In the above formula, if m = 0, n = 4; if m = 1, n = 3; if m = 2, n = 2; A is carbon or silicon; D is oxygen or nitrogen or a carboxylic group; X is oxygen or sulfur; s and t are independently 1 to 20; R1 and R2 are independently hydrogen, alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, cycloalkynyl, aryl, heterocyclic, heterocycloalkyl, cycloalkenyl, heteroaryl, alkoxyaryl, alkoxyalkyl; and B is independently arylene, arylene ether, alkylene-arylene, alkylene-arylene alkylene, alkenylene-arylene, alkenylene-arylene alkenylene, alkylene-arylene-alkenylene, alkynylene-arylene Alkynylene, Heteroarylene, Alkylene - Heteroarylene, Alkylene - Heteroarylene - Heteroarylene - Alkylene, Alkenylene - Heteroarylene, Alkenylene - Heteroarylene - Alkenylene, Alkylene - Heteroarylene - Alkenylene, Alkynylene Heteroarylene, Alkynylene - Heteroarylene - Alkynylene, Alkylene, Alkylene - Hetero - Alkylene, Alkenylene, Alkenylene - Hetero - Alkenylene, Alkylene - Hetero - Alkenylene, Alkynylene, Cycloalkylene, Alkylene - Cycloalkylene, Alkylene - Cycloalkylene Alkylene, Alkenylene - Cycloalkylene, Alkenylene Cycloalkylene - Alkenylene, Alkylene - Cycloalkylene Alkenylene, Alkynylene - Cycloalkylene, Alkynylene Cycloalkylene - Alkynylene, heterocycloalkylene, alkylene heterocycloalkylene, alkylene - heterocycloalkylene alkylene, alkenylene - heterocycloalkylene, alkenylene heterocycloalkylene - alkenylene, alkylene heterocycloalkylene - alkenylene, alkynylene heterocycloalkylene - alkenylene, alkynylene heterocycloalkylene, alkynylene - heterocycloalkylene alkynylene, cycloalkenylene, alkylene - cycloalkenylene, alkylene - cycloalkenylene, alkylene - cycloalkenylene - alkylene, alkenylene - cycloalkenylene, alkenylene - cycloalkenylene - alkenylene, alkylene cycloalkenylene - alkenylene, alkynylene - cycloalkenylene,Alkynylene - Cycloalkenylene - Alkynylene, Heterocycloalkenylene, Alkylene - Heterocycloalkenylene, Alkylene - Heterocycloalkenylene - Alkylene, Alkenylene - Heterocycloalkenylene, Alkenylene - Heterocycloalkenylene - Alkenylene, Alkylene - Heterocycloalkenylene - Alkenylene, Alkynylene Heterocycloalkenylene, Alkynylene - Heterocycloalkenylene, Alkynylene.,

[0050] In one embodiment, the recyclable epoxy resin component of formula (3), formula (4) or a combination thereof is used with a conventional curing agent selected from the group consisting of aliphatic amines, alicyclic polyamines, aromatic amines, polyether amines, ketoamines, anhydrides, polyamides, imidazoles, polythiols, polyphenols, polycarboxylic acids, carboxylic-based polyesters, carboxylic-based polyacrylates, UV curing agents, aqueous curing agents, and combinations thereof.

[0051] In one embodiment of the dissolution process, the epoxy thermosetting resin is reduced in size before being dissolved in an acid solution. Size reduction is achieved using a shredder, a milling unit, a grinder, a mixer, a crusher, or a combination thereof.

[0052] In one embodiment, the present invention is a recyclable thermoplastic component obtained using a melting process as described in the claims and disclosed above.

[0053] According to another embodiment, the present invention is a system for recycling an epoxy thermosetting resin comprising at least one recyclable component, wherein

[0054] A dissolution subsystem configured to dissolve an epoxy thermosetting resin in an acid solution under heated conditions to form a thermoplastic mixture;

[0055] A filtration subsystem configured to filter a thermoplastic mixture to separate a reinforcing matrix component from a thermoplastic solution; and

[0056] A system comprising a devolatilization subsystem configured to obtain a recyclable thermoplastic component by removing an acid solution from a thermoplastic solution, and

[0057] Here, the devolatilization subsystem includes an extruder, a falling film evaporator, a distillation unit, or a combination thereof.

[0058] In one embodiment of the system, the devolatilization subsystem is configured to remove the solvent from the thermoplastic solution. In one embodiment, the system is configured to recycle the removed acid solution, solvent, or both in the process. In one embodiment, the system is configured to be continuous or batch-based. In a preferred embodiment, the system is continuous.

[0059] According to another embodiment, the present invention is a process for recycling an epoxy thermosetting resin containing a recyclable component, wherein

[0060] A step of dissolving an epoxy thermosetting resin in an acidic solution to induce at least partial dissolution of the epoxy thermosetting resin to form a thermoplastic mixture; and

[0061] The process includes the step of devolatilizing a thermoplastic mixture to remove an acid solution and obtaining a recyclable thermoplastic component containing a reinforcing matrix component.

[0062] Such a process is an industrial non-dissolving process, in which the partial dissolution of an epoxy thermosetting resin occurs in an acidic solution to induce the formation of a thermoplastic mixture. The non-dissolving process does not filter the reinforcing matrix component from the thermoplastic solution, but the acid is removed by devolatilization. Thus, a reinforced recyclable thermoplastic component is produced that can be recycled and / or reused as another product. The recyclable thermoplastic component produced using the above process can be compounded or extruded by reactive extrusion for the manufacture of various grades of usable thermoplastic materials.

[0063] In one embodiment of the non-dissolving process, the epoxy thermosetting resin is reduced in size before being dissolved in an acid solution. Size reduction is achieved using a grinder, a milling unit, a grinder, a mixer, a crusher, or a combination thereof. In one embodiment of the non-dissolving process, immersion of the epoxy thermosetting resin in the acid solution is performed under heated conditions of 50°C to 110°C. The process is performed at 100°C.

[0064] In one embodiment of a non-dissolving process, the acid solution is acetic acid, lactic acid, propionic acid, any other aliphatic acid, any other organic acid, sulfuric acid, phosphoric acid, any other inorganic acid, or a combination thereof, wherein acetic acid is present at a concentration of 5 to 70%, lactic acid is present at a concentration of 20 to 80%, sulfuric acid is present at a concentration of 1 to 10%, and phosphoric acid is present at a concentration of 20 to 90%. According to a preferred embodiment, the acid solution is 10 to 15% acetic acid, 50% lactic acid, or 85% phosphoric acid. In one embodiment of a non-dissolving process, the acid solution contains a solvent selected from water, butanol, isopropanol, propanol, ethanol, methanol, benzyl alcohol, ethylene glycol, dichloromethane, tetrahydrofuran, ethyl acetate, acetone, dimethylformamide, acetonitrile, dimethyl sulfoxide, nitromethane, propylene carbonate, pentane, hexane, cyclohexane, benzene, toluene, xylene, dioxane, glyme, polyether, diethyl ether, any other nonpolar solvent, any other polar aprotic solvent, any other polar protic solvent, and combinations thereof.

[0065] In one embodiment of the non-dissolving process, the removed acid solution, solvent, or both are recycled back into the process.

[0066] In one embodiment of a non-dissolving process, an epoxy thermosetting resin is prepared from a diepoxy resin and a recyclable acid-unstable curing agent, wherein the recyclable acid-unstable curing agent is an amine-based curing agent, a thiol-based curing agent, a polyamino compound, any other acid-unstable curing agent, or a combination thereof; and the recyclable epoxy resin and curing agent are, wherein the recyclable epoxy resin comprises an acid-degradable acetal, ketal, orthocarbonate, orthoester, orthosilicate, or silane linkage. In one embodiment, the recyclable acid-unstable curing agent is a compound of formula (1), formula (2), or a combination thereof. In one embodiment, the recyclable epoxy resin component is a compound of formula (3), formula (4), or a combination thereof.

[0067] In one embodiment of a non-dissolving process, the reinforcing matrix component comprises glass fibers, carbon fibers, aramid fibers, jute, grass, bamboo, pine, balsa, any other natural fibers, and combinations thereof.

[0068] In one embodiment, the present invention is a recyclable thermoplastic component obtained using a non-melting process as claimed in the claims and disclosed herein.

[0069] According to another embodiment, the present invention is a system for recycling an epoxy thermosetting resin containing a recyclable component, wherein

[0070] A dissolution subsystem configured to dissolve an epoxy thermosetting resin in an acid solution to form a thermoplastic mixture; and

[0071] A system comprising a devolatilization subsystem configured to remove an acid solution from a thermoplastic mixture to obtain a recyclable thermoplastic component including a reinforcing matrix component, and

[0072] Here, the devolatilization subsystem includes an extruder, a falling film evaporator, a distillation unit, or a combination thereof.

[0073] In one embodiment of the system, the devolatilization subsystem is configured to remove the solvent from the thermoplastic solution. In one embodiment, the system is configured to be continuous or batch-based. In a preferred embodiment, the system is continuous. In one embodiment, the system is configured to recycle the removed acid solution, solvent, or both back into the process.

[0074] The epoxy thermosetting resin dissolved using this process includes, but is not limited to, epoxy thermosetting resins from manufacturing waste, epoxy thermosetting resin composites, or epoxy thermosetting resins. The composites include a reinforcing matrix and optionally non-recyclable components. The epoxy thermosetting resin may also consist of additives such as pigments, flexibilizers, tougheners, surface modifiers, fillers, foaming agents, curing catalysts, accelerators, and combinations thereof.

[0075] In the process disclosed herein, a neutralization step is not required because the acid solution (e.g., acetic acid) and / or the solution from the thermoplastic solution or thermoplastic mixture evaporates in the devolatilization subsystem. Devolatilizing the thermoplastic solution or thermoplastic mixture removes the acid solution to obtain a recyclable thermoplastic component.

[0076] The previously described recycling method utilizes the neutralization of an acid (e.g., acetic acid) in a thermoplastic solution / thermoplastic mixture, and neutralization is technically easier than devolatilization. The present invention comprises passing a filtered thermosetting resin solution or thermoplastic mixture through a devolatilization extruder to remove any excess solvent and / or acid (catalyst) without requiring neutralization. Thus, the process reduces environmental impact because sodium acetate, a byproduct of the neutralization method of the prior art, is not produced. The cost of the process is also reduced due to the reduction of unit processes. Additionally, the devolatilized acid solution, solvent, or both can be recycled back into the process, further adding to the economic advantages of the process.

[0077] FIG. 1 illustrates a specific example of the process for recycling an epoxy thermosetting resin, wherein the epoxy thermosetting resin is completely dissolved. The specific example of the dissolution process of FIG. 1 involves recycling an epoxy thermosetting resin containing at least one recyclable component, comprising immersing the epoxy thermosetting resin in an acidic solution after heating conditions of 50 to 110°C to induce dissolution of the epoxy thermosetting resin and form a thermoplastic mixture (101). In one specific example, prior to dissolution in the acidic solution, the epoxy thermosetting resin may be reduced in size into smaller pieces, because this enables more effective decomposition and, consequently, more rapid dissolution. Next, the acidic thermoplastic mixture is filtered to separate the reinforcing matrix component and optionally non-recyclable component from the thermoplastic solution (102). The thermoplastic solution is devolatilized to remove the acidic solution and obtain a recyclable thermoplastic component (103). The recyclable thermoplastic component obtained using the above process can be compounded or extruded by reactive extrusion to manufacture various grades of usable thermoplastic materials. One of the advantages of this process is that the acid solution from the acidic thermoplastic solution can be simply evaporated without the need for neutralization by corrosive substances. This enables the reuse of the acid and generates no waste. During testing, the dissolution process made it possible to completely recover the carbon fiber cloth (reinforcement matrix component) in a state close to its original condition.

[0078] FIG. 2 illustrates a specific example of the process for recycling epoxy thermosetting resin, wherein the epoxy thermosetting resin is at least partially dissolved. The non-dissolving process involves immersing the epoxy thermosetting resin in an acidic solution to induce at least partial dissolution of the epoxy thermosetting resin, thereby forming a thermoplastic mixture (201) to recycle the epoxy thermosetting resin containing recyclable components. In one embodiment, prior to dissolution in the acidic solution, the epoxy thermosetting resin may be reduced in size into smaller pieces, because this enables more effective decomposition and, consequently, more rapid dissolution. Next, the acidic thermoplastic mixture is devolatilized to remove the acidic solution, thereby obtaining a recyclable thermoplastic component containing a reinforcing matrix component (202). The recyclable thermoplastic component obtained using the above process may be compounded or extruded by reactive extrusion for the manufacture of various grades of usable thermoplastic materials. In a non-dissolving process, fibers cannot be recovered, which may be a preferred option when fibers are inexpensive (e.g., glass fibers). One of the advantages of this process is that the acid solution from the acidic thermoplastic solution can be simply evaporated without the need for neutralization by corrosive substances. This enables the reuse of the acid and generates no waste.

[0079] FIG. 3 illustrates a specific example of the process for recycling epoxy thermosetting resin, wherein the epoxy thermosetting resin is completely dissolved (a dissolution process apparatus). The apparatus in this specific example contains epoxy waste from which metallic parts have been removed using a metal detector after passing through a crusher. The residual epoxy waste is passed into a dissolution subsystem (301) configured to dissolve the epoxy thermosetting resin in an acidic solution under heated conditions to form a thermoplastic mixture. The acidic thermoplastic mixture is passed through a filtration subsystem (302) configured to filter the thermoplastic mixture to separate the reinforcing matrix components and any non-recyclable components from the thermoplastic solution. Subsequently, the thermoplastic solution is passed through a devolatilization subsystem (303) configured to remove the acidic solution from the thermoplastic solution to obtain recyclable thermoplastic components. The devolatilization subsystem may include an extruder, a falling film evaporator, e.g., the organic acid evaporation tank used in this embodiment, a distillation unit, or a combination thereof. The organic acid (and the solvent, if used) is recycled back into the process, making the process technically and economically advantageous. The apparatus is preferably continuous. The apparatus was designed to convert epoxy into a thermoplastic material by immersing epoxy waste in acetic acid solutions of varying concentrations from 5% to 50% for 1 to 3 days at various temperatures ranging from 20 to 100°C. Other acids tested and found effective were lactic acid and propionic acid. Recycling at high temperatures, such as 100°C, requires designing a sealed vessel capable of handling the pressure generated by boiling (high-pressure grade recycling equipment is required). The apparatus reduced unpleasant odors caused by rapid evaporation at higher temperatures and reduced solution loss.

[0080] FIG. 4 illustrates an embodiment of the present system for recycling epoxy thermosetting resin, wherein the epoxy thermosetting resin is at least partially dissolved (non-dissolving process apparatus). The apparatus in this embodiment comprises epoxy waste from which metallic parts have been removed using a metal detector after passing through a crusher. The residual epoxy waste is passed into a dissolving subsystem (401) configured to partially dissolve the epoxy thermosetting resin in an acidic solution to form a thermoplastic mixture; and a devolatilization subsystem (402) configured to remove the acidic solution from the acidic thermoplastic mixture to obtain a recyclable thermoplastic component including a reinforcing matrix component. The devolatilization subsystem may include an extruder, a falling film evaporator, a distillation unit, or a combination thereof as illustrated in this embodiment.

[0081] Figure 5a illustrates graphic data on the effect of different concentrations of acetic acid over time on the recycling of epoxy waste at 60°C. Figure 5b illustrates graphic data on the effect of different concentrations of acetic acid over time on the recycling of epoxy waste at 80°C. Figure 5c illustrates graphic data on the effect of different concentrations of acetic acid over time on the recycling of epoxy waste at 100°C. Higher concentrations of acetic acid enable faster recycling at 60°C, 80°C, and 100°C. At the boiling temperature (100°C), there is a dramatic effect on the recycling rate. 12.5% ​​acetic acid at the boiling temperature (100°C) induces complete recycling within 2 hours. In the case of higher concentrations of acetic acid, the increase in temperature reduces the recycling time; 50% acetic acid takes about 8 hours at 60°C (not shown), but takes only 2 hours to complete recycling at 80°C. The rate of any chemical process increases with increasing temperature. However, in the case of low concentrations of acetic acid, recycling is very slow (e.g., 10% acetic acid at 60°C induces recycling of only 20% of the mass within 6 hours) or does not occur at all (e.g., 5% acetic acid does not proceed within 3 hours), but surprisingly, at 100°C, recycling is completed within just 3 hours with 10% acetic acid, and half is completed with 5% acetic acid. Therefore, the temperature and concentration of acetic acid have been optimized to reduce recycling time while using low concentrations of acetic acid. During recycling, the viscosity of the solution increases at acetic acid concentrations of 25%, 50%, and above. At 10 to 15% acetic acid, the plastic solution does not have very high viscosity and can be reused for subsequent recycling.

[0082] The epoxy industry faces sustainability concerns, particularly regarding the waste management of end-of-life epoxy composites. Furthermore, significant value loss occurs due to large and unrecoverable manufacturing waste. Immediate recycling processes are industrially viable and scalable recycling and recovery processes that address these issues. While various acids can be used, the use of inexpensive weak acids, such as acetic acid and lactic acid at high temperatures for this purpose makes the process industrially relevant.

[0083] The present invention relates to an industrially viable recycling process for a recyclable epoxy thermosetting resin comprising a cutable linkage, the process comprising the steps of dissolving the epoxy thermosetting resin using an acidic solution and devolatilizing the acidic solution from a thermoplastic acidic mixture to produce a thermoplastic component. This process is environmentally and economically advantageous and allows for the efficient recovery of the thermoplastic component and optionally the reinforcing matrix component, both of which can be recycled for further use.

[0084] Although the present invention has been described with respect to specific embodiments, it will be obvious to those skilled in the art that various changes and modifications can be made without departing from the scope of the invention as defined in the following claims.

Claims

Claim 1 A process for recycling an epoxy thermoset comprising at least one recyclable component, comprising: i. dissolving the epoxy thermoset in an acid solution under heated conditions of 50 to 110°C to induce the formation of a thermoplastic mixture; ii. filtering the thermoplastic mixture to separate a reinforcement matrix component from the thermoplastic solution; and iii. devolatizing the thermoplastic solution to remove the acid solution in order to obtain a recyclable thermoplastic component; wherein the epoxy thermoset is prepared from a diepoxy resin and a recyclable acid-unstable curing agent, and the recyclable acid-unstable curing agent is an amine-based curing agent, a thiol-based curing agent, a polyamino compound, or a combination thereof; A process prepared from a recyclable epoxy resin and a curing agent, wherein the recyclable epoxy resin comprises an acid-degradable acetal, ketal, orthocarbonate, orthoester, orthosilicate, or silane linkage; and the acid solution comprises acetic acid at a concentration of 5 to 70% w / w and lactic acid at a concentration of 20 to 80% w / w. Claim 2 A process according to claim 1, wherein the filtration comprises the sorting of components by centrifugation, manual sorting, optical sorting, or a combination thereof. Claim 3 A process according to claim 1, wherein the acid solution comprises a solvent selected from water, butanol, isopropanol, propanol, ethanol, methanol, benzyl alcohol, ethylene glycol, dichloromethane, tetrahydrofuran, ethyl acetate, acetone, dimethylformamide, acetonitrile, dimethyl sulfoxide, nitromethane, propylene carbonate, pentane, hexane, cyclohexane, benzene, toluene, xylene, dioxane, glyme, polyether, diethyl ether, and combinations thereof. Claim 4 A process according to claim 1 or claim 3, wherein the removed acid solution, the solvent contained in the acid solution, or both are recycled back into the process. Claim 5 The process of claim 1, wherein the reinforcing matrix component comprises glass fiber, carbon fiber, aramid fiber, jute, grass, bamboo, pine, balsa, and combinations thereof, and is recyclable. Claim 6 A system for recycling an epoxy thermosetting resin comprising at least one recyclable component according to the process described in claim 1, comprising: i. a dissolution subsystem configured to dissolve the epoxy thermosetting resin in an acid solution under heated conditions to form a thermoplastic mixture; ii. a filtration subsystem configured to filter the thermoplastic mixture to separate a reinforcing matrix component from the thermoplastic solution; and iii. a devolatilization subsystem configured to remove the acid solution from the thermoplastic solution to obtain a recyclable thermoplastic component, wherein the devolatilization subsystem comprises an extruder, a falling film evaporator, a distillation unit, or a combination thereof. Claim 7 A system according to claim 6, wherein the devolatilization subsystem is configured to remove the solvent from the thermoplastic solution. Claim 8 A system according to claim 6 or claim 7, configured to be continuous or batch-based, and configured to recycle the removed acid solution, the solvent contained in the acid solution, or both of these back into the process. Claim 9 A process for recycling an epoxy thermosetting resin containing recyclable components, comprising: i. dissolving the epoxy thermosetting resin in an acid solution to induce at least partial dissolution of the epoxy thermosetting resin to form a thermoplastic mixture; and ii. devolatilizing the thermoplastic mixture to remove the acid solution to obtain a recyclable thermoplastic component containing a reinforcing matrix component; wherein the epoxy thermosetting resin is prepared from a diepoxy resin and a recyclable acid-unstable curing agent, and the recyclable acid-unstable curing agent is an amine-based curing agent, a thiol-based curing agent, a polyamino compound, or a combination thereof; or wherein the recyclable epoxy resin is prepared from a recyclable epoxy resin and a curing agent, and the recyclable epoxy resin comprises an acid-degradable acetal, ketal, orthocarbonate, orthoester, orthosilicate, or silane linkage; and wherein the acid solution comprises acetic acid at a concentration of 5 to 70% w / w and lactic acid at a concentration of 20 to 80% w / w. Claim 10 In claim 9, the process in which the epoxy thermosetting resin is reduced in size before dissolving in an acid solution. Claim 11 A process according to claim 9, wherein the immersion of the epoxy thermosetting resin in the acid solution is performed under heated conditions of 50°C to 110°C. Claim 12 A process according to claim 9, wherein the acid solution comprises a solvent selected from water, butanol, isopropanol, propanol, ethanol, methanol, benzyl alcohol, ethylene glycol, dichloromethane, tetrahydrofuran, ethyl acetate, acetone, dimethylformamide, acetonitrile, dimethyl sulfoxide, nitromethane, propylene carbonate, pentane, hexane, cyclohexane, benzene, toluene, xylene, dioxane, glyme, polyether, diethyl ether, and combinations thereof. Claim 13 A process according to claim 9 or claim 12, wherein the removed acid solution, the solvent contained in the acid solution, or both are recycled back into the process. Claim 14 A system for recycling an epoxy thermosetting resin comprising a recyclable component according to the process described in claim 9, comprising: i. a dissolution subsystem configured to dissolve the epoxy thermosetting resin in an acid solution to form a thermoplastic mixture; and ii. a devolatilization subsystem configured to remove the acid solution from the thermoplastic mixture to obtain a recyclable thermoplastic component comprising a reinforcing matrix component, wherein the devolatilization subsystem comprises an extruder, a falling film evaporator, a distillation unit, or a combination thereof. Claim 15 A system according to claim 14, wherein the devolatilization subsystem is configured to remove a solvent from a thermoplastic mixture. Claim 16 A system according to claim 14 or claim 15, wherein the system is configured to be continuous or batch-based and configured to recycle the removed acid solution, the solvent contained in the acid solution, or both of these in the process. Claim 17 delete Claim 18 delete Claim 19 delete Claim 20 delete Claim 21 delete Claim 22 delete

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